Nature Tech_2of3_The Material World
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00:00The natural world is full of the most amazing materials.
00:20Tougher than steel, finer than our best optics, and how nature builds with these materials
00:34is even more extraordinary.
00:50In the last few years, scientists have begun to look at nature with new eyes and what they're
00:57finding promises new materials, warmer, smarter, stronger, more eco-friendly.
01:27Technology, working with nature to build a new and unexpected world.
01:57For thousands of years, people have been making use of nature's raw materials.
02:24In the early days, we relied on them for our homes, our clothes, just about everything.
02:32But humans aren't the only creatures to use natural building materials.
02:41Here in northern Namibia, a pair of hornbills have used mud to make their nests secure.
02:48The female has been sealed into the nest hole behind a wall of mud, leaving just a small
02:53gap, big enough for her mate to pass food to her, but small enough to keep out all predators.
03:13Mud is a really popular choice when it comes to building.
03:17Throughout the tropics, colonies of termites use mud to produce complex nests, some standing
03:23up to three meters tall, full of intricate tunnels and chambers.
03:30To create these incredible structures, termites mix different types of mud to do different
03:35jobs.
03:38Mud mixed with saliva and feces dries to create an outer wall as strong as concrete.
03:57People have also been using mud for centuries and have found, like termites, that mud mixed
04:02with various other substances produces building materials with different properties.
04:09It's a versatile building material and it's been used to create some extraordinary things.
04:17The Great Mosque in Jena, in Mali, the world's biggest structure made of mud bricks.
04:24This impressive building is made of sun-dried mud bricks held together with a mud mortar,
04:29then coated with a plaster of smooth mud.
04:32The mosque is nearly a hundred years old and will last for centuries more if properly maintained.
04:40The Malians and termites hit on the same solutions to building by trial and error, but when biomimetic
04:47scientists look at natural materials, they're hoping not just to copy nature, but to understand
04:53the basic principles behind nature's success and build on that to invent completely new
04:59materials.
05:01And that's exactly what's happened with wood, an even more versatile material than mud.
05:11Wood is made of long, tough fibres and is used by wasps to make their nests.
05:25Chewed to a pulp and mixed with saliva, they turn it into a kind of cardboard.
05:36It's tough, it's good insulation.
05:38In short, an excellent building material.
05:45And the wasps are surrounded by it.
05:53Wood is everywhere, just for the taking, which is why it's been so useful to us.
06:01It's been used for everything from Stone Age monuments, to houses and bridges, to carts
06:07and boats.
06:10It's not surprising that wood was the foundation of our world.
06:37Unlike mud, wood is a complex, sophisticated material.
07:05It has to be, because it supports nature's largest structures.
07:15On the slopes of the Sierra Nevada mountains in California are the biggest organisms ever
07:20to have lived.
07:28These sequoias tower up to 80 metres above the forest floor, though some reach as high
07:33as 100 metres.
07:51These massive trees weigh around 1,400 tonnes, and each one contains enough timber to build
07:56120 houses.
07:59It's taken them more than 2,000 years to get to this size, and that's only possible
08:05because wood is such an amazing material.
08:18The fibres that make up wood are long, tiny, hollow tubes that carry water from the roots
08:24to the leaves, the tree's plumbing system.
08:27And around the tubes, in a helical pattern, tiny fibres of cellulose are embedded in a
08:32kind of resin.
08:34It's this arrangement that gives wood such amazing properties.
08:41In particular, this structure makes wood very resistant to cracking, crucial if a tree isn't
08:46to lose its branches in every storm.
09:02If the force on a branch is enough to start a crack, the crack just runs around the spiral
09:07fibres, which absorb its energy and stop it spreading any further.
09:15This makes wood very hard to crack, which is why we still use it today as a building
09:20material.
09:26But can we do better than nature?
09:33At the University of Reading in the UK, scientists are studying wood's performance in detail.
09:40Different kinds of wood are tested to destruction, driven by a high-pressure air system, a metal
09:45rod is rammed into a block of wood, as the scientists identify which kinds of wood are
09:51the strongest.
10:09Based on their results, they came up with a revolutionary new material, a kind of artificial
10:15wood.
10:18It's made from resin with fibres running through it, and so mimics the pattern of wood, with
10:23many of its tough properties.
10:26So much so, it's one of the toughest materials ever made.
10:31It's yet to be put to practical use, but it's strong enough to make bulletproof armour.
10:38But wood is more than just tough.
10:42It can also be smart.
10:51Like the wood in tree trunks, the woody scales of pine cones are made of stiff fibres embedded
10:56in a resinous substance.
10:58But these fibres lie in different directions in the top and bottom layers.
11:05When the scales dry out, the bottom layer shrinks more than the top, which makes the
11:10cone open and release its seeds.
11:26One designer is looking at a clothing fabric that works in the same way.
11:32As the fabric starts to get damp from sweat, sections of the fabric lift up to provide
11:38ventilation.
11:43This is true biomimetic thinking.
11:46Not merely using natural materials, but understanding how they work, and applying the principle
11:52somewhere else.
12:08But this kind of thinking isn't entirely new.
12:12Natural designs inspired some of the Victorian age's greatest architecture.
12:25In 1849, botanist Joseph Paxton had to build a new and bigger greenhouse for his ever-expanding
12:33Victoria lilies.
12:38These plants produce enormous leaves, up to two metres across, hence Paxton's problem.
12:48But those same leaves held the solution to his problem.
12:54They're supported by a complex series of ridges and struts, and Paxton saw he could use the
13:00same arrangement to support a large roof span over his new greenhouse.
13:06He showed just how strong these leaves were in a most unusual way.
13:11They can easily cradle a baby.
13:21Paxton was so confident of the leaf's strength, he entrusted his young daughter to this Victorian
13:26equivalent of a waterbed.
13:32When full-sized, these leaves can even support the weight of an adult.
13:42He built his greenhouse on these bio-inspired principles, and it was so successful that
13:49he went on to build even bigger structures, like the magnificent Crystal Palace.
13:55Built in London for the first World's Fair in 1851, the Crystal Palace was a technological
14:00marvel of glass and iron, 33 metres high and covering about seven hectares, all thanks
14:08to a plant from the depths of the Amazon rainforest.
14:14What the lily shows is that it's not just the material used that makes it tough.
14:19It's also the details of how it's constructed, and that's equally true of the materials that
14:26make up animals.
14:34When the fall comes to the Rocky Mountains of North America, nature puts on a dramatic
14:38demonstration of one of her most remarkable materials.
14:48At this time of year, male elk gather up groups of females ready to mate, but they have to
14:54defend these harems from rivals.
15:06For that purpose, nature has provided them with tough antlers made of bone.
15:22Despite energetic wrestling, broken antlers are very rare.
15:29But bone is heavy, so nature is as economical as possible.
15:34Inside, bones are partly hollow, but filled with a complex network of arches and spans.
15:42This beautiful hidden structure is also elegant engineering.
15:52The bony struts are laid down along lines of stress in the bone, so it's strongest where
15:58it feels the biggest loads.
16:00It's as strong as it can be, but using the minimum of material.
16:07Even our own skeletons can be a source of inspiration.
16:16The human thigh bone, or femur, is especially elegant.
16:21The head of the bone is off to one side, which means the weight of the body has to be transferred,
16:26first sideways, then down the length of the bone.
16:32Struts of bone arch through the head of the femur, transferring this weight both effectively,
16:37and economically.
16:45And architects realized they could apply exactly these principles in constructing tall buildings.
16:56It's the inspiration behind one of the most famous buildings in the world, the Eiffel
17:01Tower.
17:07Gustav Eiffel used the structure of the human thigh bone in building his 300-meter tower,
17:14the tallest building in the world until 1930.
17:20Like the curve in the head of the femur, the famous iron curves of the Eiffel Tower are
17:25supported by a latticework of metal struts and girders that transfer the tower's weight
17:31sideways and down to the ground, just as elegantly as the internal struts of bone.
18:01In recent years, more and more designers and engineers are looking at the way nature builds
18:06bodies, and getting inspiration for everything from new bridges and buildings to cars.
18:16Cars need to be tough, but can't be too heavy or they burn too much fuel.
18:22Nature faces the same problem, which is why both animals and plants only lay down material
18:27precisely where they need it.
18:32So this car-shaped fish, the boxfish, might be a good model for an economic car.
18:42And when the engineers at Daimler-Chrysler designed a chassis using a computer program
18:46that, like the boxfish, laid down more material where the loads were greatest, they found
18:52they'd made their lightest, strongest chassis ever.
19:00For vertebrates, like fish, mammals and birds, the skeleton gets its strength from the material
19:06of bone and the way it's constructed.
19:12Vertebrates are built around the outside of these internal bony struts, a system that
19:16works well for the biggest animals, like these moas, giant extinct birds.
19:23But there are other types of skeleton.
19:29Insects are the other way round.
19:33Their skeleton is on the outside, an exoskeleton.
19:37An insect is hung from the inside of a tough protective casing, the optimum engineering
19:43solution for small creatures.
19:48Bones are strengthened with deposits of heavy calcium phosphate, but tiny insects can't
19:53afford so much weight.
19:56Natural selection has had to come up with a lightweight solution, a structure made of
20:00fibres of a substance called chitin, embedded in a matrix.
20:07Like plywood, each layer of fibres runs at a slightly different angle, making the exoskeleton
20:13very strong in every direction.
20:17Tough enough for male stag beetles to use their jaws like the antlers of an elk, wrestling
20:22with each other over females.
20:26Other insects use their jaws for their original purpose, for eating.
20:36Locusts eat grass, lots of grass.
20:41Grass leaves are protected by tiny crystals of silica, which wear away most substances.
20:47But the jaws of a locust can cope.
20:51And before they're in danger of wearing out, a young locust can replace them by shedding
20:58its whole outer casing.
21:06Insect cuticle is remarkable stuff.
21:10So what can we do with it?
21:14First we need more than we can get from tiny insects.
21:20But on the east coast of North America, a huge supply of chitin crawls out of the water
21:25onto the beach every spring.
21:32Horseshoe crabs are not insects, but neither are they crabs.
21:37They're primitive creatures related to spiders that have swarmed onto beaches to spawn like
21:42this for hundreds of millions of years.
21:45But like insects, their shells are strengthened with chitin fibers.
21:50They were collected for their shells, but over-collecting has reduced their population.
21:56Not a good way to work hand-in-hand with nature.
22:04Fortunately, the eastern seaboard of the United States offers up another chitin bounty.
22:11And most of this is going to be thrown away.
22:13A much better source.
22:18Crab factories around North America's Chesapeake Bay extract the valuable meat for canning.
22:23But the shells themselves could be just as valuable.
22:27The shells of crabs also contain lots of chitin, but it's bound up with calcium carbonate.
22:33However, by treating the shells with acid, this can be dissolved, releasing the chitin for use.
22:49By purifying the chitin and chemically altering the fibers, a substance called chitosan can be made.
22:59In its purest form, it's used to make contact lenses, skin creams, and wound dressings.
23:14But chitosan can also fill many of the purposes of plastic.
23:34And even better than plastic, it's biodegradable.
23:41But smashing up this amazing substance and converting it into a bioplastic may not be the best way of exploiting its potential.
23:51An insect's exoskeleton is a marvel of microengineering and almost endlessly versatile.
23:58It can be shaped to resemble a leaf with amazing accuracy, living or dead.
24:09Even down to the holes chewed by other insects.
24:31The level of detail is extraordinary.
24:43Hidden in this orchid flower is an orchid mantis.
24:49Its body and legs are sculpted and colored to match the petals of the flower exactly.
24:55It's virtually invisible to its predators and to its prey.
25:14But look even closer and the insect's body armor is even more astounding.
25:20Molded and shaped with microscopic precision into a huge variety of shapes.
25:27And it's not just there to admire.
25:29Each of these microscopic landscapes has a job to do.
25:35These tiny bumps cover the body of a beetle that lives in the Namib Desert.
25:43In this parched desert, it hardly ever rains, yet beetles seem to flourish here.
25:50Their only supply of water is the fog that rolls in from the ocean every morning.
25:55So the beetles start each day by climbing to the top of a dune,
25:59where they can intercept the fog blowing in on the wind.
26:17Those microscopic bumps help water condense on their bodies.
26:22The tips of the bumps attract water, while the channels between repel it.
26:28This forces the water to form droplets which run down to the beetle's mouth.
26:34A desert survival strategy that might help with all too frequent water crises in the
26:40human world.
26:43One company is now designing tents for refugees that work in the same way.
26:50These tents could condense water from the air each morning,
26:53even in areas where groundwater is in short supply.
26:59In this case, understanding how a desert beetle lives could make all the difference between
27:05life and death for these people.
27:09And all this comes from the extraordinary design of insect skeletons.
27:16Yet this whole complex structure is shed and replaced every time the insect molts,
27:22which seems something of a waste.
27:42Insects can afford to do this because the arrangement of chitin fibres is self-assembled.
27:48When the right components come together in the right way, the exoskeleton just builds
27:53itself.
27:56And this kind of self-assembly process is very interesting to biomimetic engineers.
28:05Crystals are a simple example of self-assembling structures.
28:09The final shape of a crystal is not due to some elegant overall design.
28:14It happens because the atoms or molecules naturally come together in a lattice that,
28:20as it grows, results in these familiar shapes.
28:24More complex molecules can self-assemble into more complex shapes.
28:32If we could control the way the component parts of a material interact, we could just
28:37mix them together, sit back, and watch the most complex of designer materials just build
28:43themselves.
28:45Impossible.
28:48Nature does it all the time.
28:50One impressive example can be seen off the coast of California.
28:56Here sea otters seem to live an idyllic life, floating on a gently rolling ocean.
29:11And when they're hungry, all they need to do is dive down to the ocean floor and pick
29:16up a tasty shellfish.
29:29But it's not that easy.
29:31Shellfish have tough shells, so tough that sea otters have to resort to a clever trick.
29:37They hammer the clam on a stone balanced on their chests, and eventually they'll get
29:43their reward.
29:52As smart as the sea otter's trick looks, it's the discarded shells that are really interesting.
29:59Why did it take so much effort for the sea otter to get its meal?
30:07After all, these shells are just made up of calcium carbonate, ordinary chalk.
30:13And that's not tough at all.
30:21The secret is in how mollusks arrange the crystals of calcium carbonate.
30:27A shell is made up of several layers, but the iridescent inner mother-of-pearl layer,
30:33the nacre, is the really spectacular part.
30:39Magnifying the shell thousands of times reveals an intricate structure.
30:44Flat crystals of calcium carbonate sitting in a matrix of protein.
30:53If one crystal cracks, the crack simply runs into the protein, which is just stretched,
30:58absorbing the energy.
31:01Eventually the protein matrix will absorb all the crack's energy and stop it dead.
31:06But the protein does more than just stopping cracks from spreading.
31:10It's responsible for the precise way in which the crystals are laid down.
31:15As the mollusk grows its shell, it secretes these proteins, which form a layer over its
31:20body.
31:22As calcium carbonate is secreted into this layer, the proteins make sure it crystallises
31:27in just the right way to form nacre.
31:33Nacre is a kind of ceramic, a tough, non-metallic structure made up of tiny crystals.
31:39Humans have been making their own ceramics for thousands of years.
31:43Pottery, for example, is also a ceramic.
31:49And apart from pots, we now use ceramics as engine parts or even tank armour.
31:57And when we make ceramics, we have to heat them to perhaps 1,400 degrees centigrade.
32:04Nature makes its ceramics at sea temperature.
32:09And what it can do is truly spectacular.
32:23These ceramics, made by humble mollusks, are twice as strong as anything we can make.
32:40Such natural flamboyance gave scientists the idea of isolating the proteins responsible
32:45for organising the way nacre is laid down.
32:48Then, by changing them, they hope to be able to grow all kinds of intricate structures.
32:54Perhaps even computer chips more powerful than any that can be made by today's methods.
33:08In the freezing cold of the high Arctic, it's not strength but warmth that's needed.
33:14Polar bears are cosy even in sub-zero temperatures.
33:18Seen with an infrared camera, the brightest areas are those losing heat, which for the
33:24polar bear is mainly its nose.
33:30The rest of its body is extremely well insulated, apart from the tips of its toes.
33:37In the snowy wastes, it's almost as well camouflaged in infrared as it is in ordinary light.
33:46The polar bear's high Arctic survival gear is its fur.
33:50Each hair is transparent and hollow.
33:53And it used to be thought that this conducted the sun's heat down to the skin.
33:58Polar bear skin is black, which absorbs this heat.
34:04Now scientists are not so sure, but it was a good idea nevertheless.
34:09So scientists at the Institute for Textile Technology at Denkendorf in Germany have developed
34:15an artificial polar bear fur that does work in this way, by conducting infrared and ultraviolet
34:22radiation down to a black base layer.
34:26These fibres on their own are not as good at insulation as polar bear fur, but a transparent
34:32layer on top improves the overall performance by trapping a layer of warm air.
34:41Wrapped around a water container, this material can warm the water just by conducting the
34:46sun's heat, even though it appears this isn't how polar bears do it.
34:55The more we look at the microscopic detail of nature's structures, the more we find
35:00they can do.
35:06All the plants in a tropical rainforest depend on these torrential downpours for survival.
35:12But they can also create problems.
35:15The rain washes down dirt, which could coat the leaves and block out light.
35:19Worse, wet leaves will soon grow a layer of mould in this warm, humid environment.
35:34Some rainforest plants have drip tips designed to drain water off the leaf.
35:46But some just don't seem to get wet at all, no matter how much it rains.
35:56This is the most spectacular, a lotus leaf.
36:01Slowed down more than a hundred times, it's clear that the water just bounces off the
36:06leaf.
36:07The water can't spread out and wet the leaf.
36:09Instead, it just reforms droplets that bounce across the leaf until they fall off.
36:40Again, the secret is in the microscopic detail of the lotus leaf.
36:53Its surface is covered in tiny bumps, each of which is capped by a waxy layer.
36:59The caps repel water, forcing it to perch on the very tips of the microscopic bumps.
37:06Unable to reach the leaf's surface, all the water can do is roll back into a sphere.
37:11And since it's repelled by the tiny bumps, there's nothing to stop it rolling off the
37:16leaf.
37:24But even more impressive, the water drops pick up any particles of dirt on the leaf's
37:29surface and carry them off as well.
37:35So lotus leaves are always immaculately clean, a reason why they're a symbol of purity in
37:42eastern religions.
37:52And it's too good a trick for science to miss.
38:00This fabric has all the water-repelling qualities of a lotus leaf.
38:16To make it means first weaving a strong, dense material.
38:33The material is then run through a machine that coats it with a substance that's still
38:38a closely guarded secret.
38:46As it dries, this coating produces millions of microscopic bumps over the surface of the
38:51material that work in the same way as those on a lotus leaf, making a material that is
38:57not only water-repellent, but self-cleaning.
39:06And there's already a self-cleaning paint based on the same principle.
39:13Ordinary paint soon gets dirty, but dirt and water just roll off this new paint called
39:20lotusan.
39:36And a similar coating over this spoon means simple, pure water will pick up any dirt and
39:41leave the spoon totally clean.
39:52The surface, developed at the University of Bonn in Germany, even repels something as
39:57sticky as honey, which just runs off like water.
40:07Won't it be great when the self-cleaning shoe is invented?
40:17Repelling water is the key to good waterproofing, and both people and nature have invented many
40:23ways of doing this.
40:39We use fabrics coated in water-repellent oils.
40:45And many birds do the same.
40:51Spreading a layer of oil over their feathers, which means the water just runs off like,
40:58well, water off a duck's back.
41:03So ducks would be the obvious place to look for improvements in waterproofing.
41:08But in biomimetics, it's not always the obvious places that are the best.
41:18Hidden beneath the surface of a South American stream, a strange spider has a novel way of
41:24waterproofing itself.
41:27These spiders prey on small fish in mountain streams, and underwater, they trap a silvery
41:33layer of air around their bodies.
41:50But when they emerge from the water, they're completely dry.
42:10Researchers at the University of Bonn in Germany have been trying to unlock the spider's secrets.
42:18The spiders are covered in bristles, and it turns out that the spacing and three-dimensional
42:23arrangement of these bristles is critical in giving the spider its extreme waterproof coat.
42:30The scientists here have measured the exact spacing of these hairs, as well as looking
42:35at the intricate microscopic architecture of the individual hairs.
42:46Using these findings, researchers have developed an ultra-waterproof fabric.
42:52As a test, it was submerged in water for four days, and still emerged bone-dry.
43:05Staying dry is certainly not a problem faced by the sandfish.
43:10This lizard lives in the most inhospitable parts of North African and Middle Eastern
43:15deserts, bare, sandy dunes.
43:28It's called the sandfish because, when it feels threatened, it can dive into the sand.
43:49It's able to swim through the dunes as if they were water, which is surprising since
43:55moving through sand should take a lot more energy than moving through water.
43:59So scientists from the Technical University of Berlin decided to take a closer look at
44:05this ability.
44:06They found the sandfish's skin had lower friction than glass or even polished steel.
44:13The sand just rolls off it, and it's not at all obvious how it performs this trick.
44:19Its shovel-shaped head certainly helps, but its ability to swim through sand seems to
44:25rely mainly on its remarkable skin.
44:30Magnified more than 25,000 times, a series of tiny spikes appears along the edge of every
44:37scale, each just a few millionths of a millimetre long.
44:42Somehow, these structures must reduce the friction between the grains of sand and the
44:47skin, though quite how is still not clear.
44:51And even stranger, these tiny structures just don't seem to get worn away by the sand.
44:59One possibility is that the spikes conduct static electricity, stopping the lizard from
45:05charging up as it rubs through the sand grains, and therefore stopping the sand grains sticking
45:11to its skin.
45:15Nature's microstructures might hold the secrets to better waterproofing or non-stick surfaces,
45:21but they might also hold the secrets to the next generation of computers.
45:28A new information revolution.
45:33A story that starts with a spectacular rainforest butterfly.
45:42The bright blue of a morpho butterfly shines out like a beacon in the rainforest.
45:48It can be seen half a kilometre away, exactly what the butterfly wants, to attract a mate.
46:05But the wings of these butterflies contain no pigments.
46:11They produce colour in the same way that soap bubbles do.
46:21These shimmering colours are caused by light being reflected from the outside and inside
46:26surface of the bubble, and change with the angle of viewing.
46:43But the colour of a morpho is far more intense than a soap bubble, and the reason is down
46:49to the micro-architecture of each and every tiny wing scale.
46:55The morpho uses these colours for display, to make itself conspicuous.
47:01And it's certainly been noticed by scientists.
47:04At Exeter University in the United Kingdom, they've been examining the morpho's micro-architecture
47:10down to the finest detail.
47:23Each scale is covered in ridges.
47:27And each ridge is made of layers of cuticle.
47:31These layers are separated by a distance that is the same as the wavelength of blue light,
47:36and so when sunlight bounces off each of these layers, only the blue light is reflected back.
47:43And the exact spacing of the layers means successive waves of blue light interfere with
47:48each other, reinforcing themselves and intensifying the colour.
48:00To make it easier to see what's happening, the Exeter scientists then built a model of
48:05this structure that will work with microwaves that have a much longer wavelength than light.
48:11And what they found was that the gaps in the ridges on the wing scales are structured in
48:15such a way that no light gets trapped.
48:19It's all reflected, which adds to the brilliance of the colour.
48:31It's hard to believe that there isn't a single molecule of pigment in these scales.
48:39Japanese manufacturers have incorporated these ideas into fabric, material they call morphotex,
48:46made up of nylon and polyester arranged in the same way as the layers of cuticle
48:51in a morpho's wing scale.
48:53Morphotex shimmers with interference colours that will never fade,
48:57and cosmetics companies are already developing lipstick with the same effect.
49:04But the morpho's lesson is even more profound.
49:11Each scale is in fact a photonic crystal, a device that can transmit light,
49:18the optical equivalent of a transistor.
49:21Transistors revolutionised electronics and powered the computer revolution.
49:27Photonic crystals could power a new information revolution of even faster,
49:32more energy efficient optical computing.
49:36And nature might well be able to point the way.
49:42With this new way of seeing the world, the possibilities are endless.
49:50Modern technology has already created a whole range of new materials based on nature's examples,
49:56but sometimes nature is still one step ahead.
50:01Spider silk is an extraordinary material, size for size, stronger than steel,
50:07but it's also highly elastic.
50:09It's made from strands of different proteins,
50:13and spiders can produce different kinds of silk depending on their need.
50:18It's stored as a liquid and solidifies into strands
50:21as it's squirted out through tiny nozzles on the spider's rear end.
50:26Yet we've never been able to copy this.
50:29Artificial spider silk is still a holy grail for biomimeticists.
50:36We'll probably succeed one day,
50:39but watching a spider spin these beautiful structures
50:42is a good reminder that it'll take some time to catch up with four billion years of evolution.
50:59The natural world is built from amazing materials,
51:03but the structures that nature produces with these materials are just as intriguing,
51:10and they hold lessons in how to manage energy efficiently and cleanly.
51:15Lessons that, at the start of the 21st century,
51:19humanity urgently needs to learn.
51:42In the next program, we'll see how nature's use of energy
51:46can offer ways to solve our energy crisis,
51:49and how information systems, more sophisticated than any we've imagined,
51:54give our computer revolution new and unexpected directions.
52:16you